Many communication systems employ one or more central communication devices such as base stations, central controllers, cable head ends or the like, with each central device serving a number of remote devices. The remote devices served by a central device may be deployed at varying distances from the central device, and may experience other variations in communication conditions that create differences in the quality of the communication channel. In addition, the remote devices may move from one location to another, moving closer to or farther from the central device, and may otherwise experience changes in conditions that alter the quality of the communication channel experienced by each and alter the relative qualities of the channels experienced by two or more remote devices.
In typical prior art systems, each remote device is allocated a fixed bandwidth. This bandwidth may be defined by a channel filter. Each remote device experiences an increase in signal to noise ratio as it experiences improvements in the communication channel, as may occur if it moves closer to a central device. The improvement in signal to noise ratio allows an increase in transmission rate, which is often achieved by matching the modulation coding technique to the channel conditions experienced by a remote device. When no power control is used, the power and bandwidth of the transmitted signal is held constant and the number of states that the particular modulation format being employed allows for use by the remote station is changed to match the current received signal quality. Allowing more states allows a remote device to encode additional symbols, allowing an increase in the number of bits transmitted.
However, the maximum possible transmission rate increases slowly with signal to noise ratio. The maximum theoretical communication rate of a communication system, expressed in bits per second, is given by the following equation:R=BW* log2((S+N)/N),  (1) whereR+communication rate, BW=bandwidth, S=signal and N=noise. Throughout this discussion, the term “noise” refers to a combination of noise and interference. Thus, the value of the variable “N” includes both noise and interference. It can be seen that the communication rate is proportional to the logarithm of the signal to noise ratio. A doubling of the signal to noise ratio yields only a 1 bit per second increase for each Hertz of bandwidth.
There exists, therefore, a need for improved systems and techniques for adjustments for changes in channel condition which allow greater increases in transmission rates with improvements in channel condition.